Above and Below: The mine tunnels are bored through almost pure salt; salt dust coats everything. At this depth in the Earth the temperature is almost a constant 95° F year round. Salt has an affinity for water and the mine air can be quite dry even though safety requires constant ventilation. As a result, workers in the mine loose fluid both through perspiration and simply by breathing. Although temperature is a bit high for the back-up batteries and electronics, the almost constant temperature means that the HKT bell jars and seismometers will not be affected by temperature fluctuations like those prevalent on the Earth's surface.